Small enterprises in Thailand often struggle with inefficient inventory management, particularly in recording serial numbers (S/N) and processing inventory transactions manually. These challenges lead to delays, resource wastage, and increased operational costs. This research aims to develop a cost-effective inventory management system tailored for small enterprises by leveraging App Sheet and Google Sheets, integrated with Lean principles to minimize waste and enhance data accuracy. The proposed system focuses on eliminating redundant processes, improving transaction speed, and reducing errors. Experimental results demonstrate that the implementation of this system reduced S/N recording errors by 85% and decreased inventory management time by 65% compared to traditional methods. Additionally, the system significantly improved data accuracy and operational efficiency. The study suggests further deployment of this solution across small enterprises seeking an affordable yet effective inventory management system to enhance accuracy and streamline operations.